In this licentiate thesis light-matter interaction between hydrogen and superintense attosecond pulses is studied. The specific aim here is to identify for what intensities the non-relativistic calculations, given by solving the time dependent Schrödinger equation, no longer are valid.
In order to do this the time dependent Dirac equation has been numerically solved for interaction beyond the so called dipole approximation, where spatial dependence of the pulse is neglected.
The spatial part of the pulse is taken into account by a power series expansion truncated at a certain order. It is shown that the relativistic description demands more terms in this expansion compared to the non-relativistic description. As spatial dependence is computationally heavy to take into account, several optimizations have been made.
As relativistic effects are expected when the classical quiver velocity of the electron reaches a substantial fraction of the speed of light, this thesis considers cases up to v≈0.23 c .